This invention relates to a process for treating ash-containing coal to remove the ash therefrom.
Naturally occurring coals have relatively high ash contents. Usually coal contains about 7 to about 25% of ash which consists chiefly of silica (SiO.sub.2), alumina (Al.sub.2 O.sub.3), etc. When observed by an X-ray microanalyzer, the ash in coal is in the form of particles about 5 .mu.m to tens of .mu.m in size. It is already known to remove such ash from coal by pulverizing the coal, mixing the pulverized coal with water to obtain a slurry, adding to the slurry an oil serving as a binder to form the coal and the oil into granules, and separating the granules from the ash-containing aqueous medium. The granules separated from the ash are pellets of oil-containing deashed coal useful as a fuel. However, the conventional process has the problem of being unable to fully remove the ash from coal, because for the full removal of the ash, the coal must be pulverized to very fine particles as small as ash particles contained therein, i.e. about 5 .mu.m to tens of .mu.m. Nevertheless, if coal is divided exceedingly finely, the particulate coal has an increased surface area, requires the use of an increased amount of the binder oil and takes a greatly prolonged period of time for granulation. Consequently it is impossible to pulverize coal to very fine particles and therefore to deash the coal to a full extent.